1. Field of the Invention
The present invention relates to an image photographing apparatus and image photographing method for imaging a distribution of radiation characteristics in an object to be examined which is obtained using an X-ray still image photographing apparatus or the like.
2. Description of the Related Art
X-ray photographing apparatuses have been known in which X-ray beams are emitted from X-ray sources and transmitted through objects to be examined such as medical subjects, and the objects are photographed after the X-ray beams pass through the objects, using screen films, computed radiography (CR) systems, flat panel detectors (FPDs) or the like.
For X-ray photographs, high-resolution solid state X-ray detectors have been developed. Such a solid state x-ray detector has an X-ray sensor in which a two-dimensional array using 500 to 10000 photoelectric conversion devices such as photodiodes are arranged in each dimension. Each photoelectric conversion device generates an electrical signal corresponding to an amount of X-rays incident on the X-ray sensor. An X-ray image is obtained by arranging the object between an X-ray source and the X-ray sensor and converting the amount of X-ray which have been transmitted through the object into an electrical signal. An electric signal from each photoelectric conversion device is read out individually and converted into a digital signal. The digital signal is then processed into an image signal, stored in a recording device, and displayed.
Conventional photographing apparatuses for capturing such X-ray images have been used primarily for still images.
As described in U.S. Pat. No. 6,947,084, for example, a recent photographing apparatus which uses a FPD is capable of reading a plurality of images in a time sequence. Thus, a plurality of images can be output in a still image photographing operation.
A processing procedure of such a still image photographing operation is illustrated in a flowchart shown in FIG. 8. When an X-ray image photographing operation is performed, an object to be examined is positioned between an X-ray generator and a digital X-ray photographing apparatus, at STEP S101. At the same time, a collimator of the X-ray generator is adjusted so that an X-ray beam is irradiated onto an appropriate range and a desired image of the object can be obtained. Thus, the position and range of the incident X-ray beam are determined.
At STEP S102, X-ray photographing is carried out. In STEP S102, an X-ray beam is projected and passes through the object. Then, the X-ray beam is irradiated on the digital x-ray photographing apparatus as an X-ray beam having an intensity distribution and converted into electric charge by a photoelectric conversion device. The electric charge is then converted into a pixel value having an intensity distribution in accordance with the transmissivity of the object. When the irradiation of the X-ray beam is completed, the signal converted by the photoelectric conversion device is read. Then, at STEP S103, a preview of an image representing image data obtained by the digital X-ray photographing apparatus is displayed on a film or a monitor. The preview image obtained in STEP S103 is examined by an operator to manually determine if rephotographing is necessary, at STEP S104. This determining process used to determine the presence or absence of motion or respiration of the object (subject) as well as to determine the presence or absence of a region of interest in the object (subject) is performed in the preview image.
At STEP S105, an image is output which can be used for diagnosing the subject. This image for diagnosis may be a film image or monitor output image. The obtained image is examined and the necessity of rephotographing is determined at STEP S106. When it is determined that rephotographing is not necessary, the processing procedure is terminated, and the subject is freed from the examining position.
As described above, in conventional photographing apparatus which uses an FPD, the necessity of rephotographing or the presence of body motion of a subject is determined by operator's visual observation of photographed image, on the basis of an image output by the photographing apparatus.
However, in such conventional photographing apparatus, the presence or absence of motion of the subject or another factor is determined after a predetermined amount of X-rays are irradiated. Therefore, wasteful operations such as rephotographing cannot be avoided every time when motion is present in a photographed image.